1. Field of the Invention (Technical Field)
The present invention relates to active inverter/rectifiers and turbine generators.
2. Background Art
Note that the following discussion refers to a number of publications by author(s) and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-a-vis the present invention. Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
Turbogenerators discussed herein often comprise a permanent magnet generator. Such permanent magnet turbogenerators typically include a compressor, a gas turbine and a bearing rotor including a permanent magnet generator. A permanent magnet turbogenerator can be utilized to provide electrical power for a wide range of utility, commercial and industrial applications. While an individual permanent magnet turbogenerator may only generate up to approximately 150 kilowatts, powerplants of up to 1 megawatts or greater are possible by linking numerous permanent magnet turbogenerators. Throughout this disclosure, microturbine power generator and permanent magnet turbogenerator are used interchangeably according to the aforementioned general description.
A microturbine power generating or xe2x80x9cpermanent magnet turbogeneratorxe2x80x9d system typically includes a turbine, a compressor and an electrical generator. Such a system is disclosed in U.S. Pat. No. 4,754,607, entitled xe2x80x9cPower Generating System,xe2x80x9d to Mackay, issued Jul. 5, 1988. Start-up of a microturbine power generating system requires a power source separate from the turbine itself to rotate the turbine/compressor, such as a battery or flywheel, which may be located within the same structure or enclosure that contains the gas turbine engine. Often, a separate starter motor is used to turn the compressor until the microturbine power generating system is capable of sustaining combustion. Alternatively, the microturbine""s electrical generator is used to turn the compressor during startup. When the microturbine""s electrical generator is used, a switch/starter control is included to supply an excitation current to stator windings of the electrical generator, which turns the compressor until combustion can be sustained. However, both approaches require an external source of power to operate the starter motor or to supply an excitation current to the stator windings of the electrical generator. A battery or a grid are suitable external sources of power for a starter motor or a switch/starter control.
U.S. Pat. No. 6,046,122, entitled xe2x80x9cMicroturbine Power of Generating System Including a Battery Source for Supplying Startup Power,xe2x80x9d to McConnell, issued May 16, 2000 (""122 patent), discloses a system having a battery based starter wherein the battery""s DC power is converted to 3 phase AC power suitable for providing an excitation current to the stator windings of a microturbine""s electrical generator. The system also has an up chopper for reducing the required output voltage of the battery and a down chopper for converting AC voltage to a DC voltage suitable for charging the battery.
In one embodiment of the ""122 patent, the system uses a low voltage battery source and a starter control including a DC link, an inverter and a bidirectional chopper. The bi-directional chopper provides the functionality of both the up chopper and the down chopper. Thus, the bi-directional chopper boosts the voltage from the low voltage battery source and applies the boosted voltage on the DC link. A second inverter converts the power on the DC link to three-phase AC power for startup using the 3 phase rotary machine in a motoring mode. During normal operation of the microturbine power generating system, the down chopper feature of the bi-directional chopper uses rectifier output power (available at the DC link) to charge the low voltage battery source. A duty cycle of 10%, for example, would reduce a rectified voltage of 500 volts to about 50 volts for charging a 48 volt battery. In the event the electric generator experiences a failure during normal operation, the bi-directional chopper can connect the battery source to inputs of a main inverter to provide backup power.
International Application, WO 98/25014, published under the Patent Cooperation Treaty, entitled xe2x80x9cElectrical System for Turbine/Alternator on Common Shaft,xe2x80x9d to Gupta et al., published Jun. 11, 1998, discloses a system that uses a single inverter and mechanical contactors in a start-up and an operational mode. A shaft sensor is also required for start-up operation.
In one embodiment, the present invention comprises a permanent magnet turbogenerator system comprising a permanent magnet turbogenerator and an active inverter/rectifier. In this embodiment, the active inverter/rectifier comprises an input for inputting a three-phase AC voltage from the permanent magnet turbogenerator, an output for outputting a DC voltage, and at least six insulated gate bipolar transistors (IGBTs), each having a corresponding anti-parallel diode, wherein selective switching of the IGBTs boosts the resulting DC voltage. According to this embodiment, the system optionally allows for output of a boosted DC voltage at a reduced turbine engine speed. Further, this embodiment optionally allows for the output of a boosted DC voltage at a reduced turbine engine speed that results in a higher turbine operating temperature and consequently a turbine operational efficiency that is greater than that achieved for output of an equivalent non-boosted, DC voltage.
In another embodiment, the present invention comprises a starter for starting a permanent magnet turbogenerator comprising a permanent magnet turbogenerator wherein the permanent magnet turbogenerator comprises a shaft connected to a turbine engine; a three-phase AC voltage source; a first active inverter/rectifier that comprises an input for inputting a three-phase AC voltage from the three-phase AC voltage source, an output for outputting a DC voltage to a DC voltage link, and at least six IGBTs, each having a corresponding anti-parallel diode, wherein selective switching of the IGBTs boosts the DC voltage to the DC voltage link; and a second active inverter/rectifier that comprises an input for inputting the DC voltage from the DC voltage link, an AC voltage output, and at least six IGBTs, each having a corresponding anti-parallel diode, wherein selective switching of the IGBTs produces a pulse width modulated AC voltage for output to the permanent magnet turbogenerator and rotating the shaft.
In yet another embodiment, the present invention comprises a battery charger for charging a permanent magnet turbogenerator starter battery. According to this embodiment, the apparatus comprises a three-phase AC voltage source; an active inverter/rectifier that comprises an input for inputting a three-phase AC voltage from the three-phase AC voltage source, an output for outputting a DC voltage to a DC voltage link, and at least six IGBTs, each having a corresponding anti-parallel diode, wherein selective switching of the IGBTs boosts the DC voltage to the DC voltage link; and a permanent magnet turbogenerator starter battery that is chargeable by connection to the DC voltage link. This embodiment optionally comprises a circuit for controlling battery charging as a function of temperature, for example, but not limited to, battery temperature.
One embodiment of the present invention comprises an active inverter/rectifier system for a permanent magnet turbogenerator. In this embodiment, the system comprises a DC voltage link; a first active inverter/rectifier that comprises a connection for inputting or outputting a three-phase AC voltage from or to an AC voltage source, another connection for inputting or outputting a DC voltage from or to a DC voltage link, and at least six selectively switchable IGBTs, each having a corresponding anti-parallel diode, capable of boosting the DC voltage; and a second active inverter/rectifier that comprises a connection for inputting or outputting a three-phase AC voltage from or to a permanent magnet turbogenerator, another connection for inputting or outputting a DC voltage from or to the DC voltage link, and at least six selectively switchable IGBTs, each having a corresponding anti-parallel diode, capable of boosting the DC voltage wherein the boost capability of the first and the second active inverter/rectifiers comprises software controlled switch drivers.
In another embodiment, the present invention comprises an active inverter/rectifier system for a permanent magnet turbogenerator. In this embodiment, the system comprises a DC voltage link; a first active inverter/rectifier that comprises a connection for inputting or outputting a three-phase AC voltage from or to an AC voltage source, another connection for inputting or outputting a DC voltage from or to a DC voltage link, and at least six selectively switchable IGBTs, each having a corresponding anti-parallel diode, capable of boosting the DC voltage; and a second active inverter/rectifier that comprises a connection for inputting or outputting a three-phase AC voltage from or to a permanent magnet turbogenerator, another connection for inputting or outputting a DC voltage from or to the DC voltage link, and at least six selectively switchable IGBTs, each having a corresponding anti-parallel diode, capable of boosting the DC voltage wherein the boost capability of the first and the second active inverter/rectifiers comprises hardware controlled switch drivers.
In yet another embodiment, the invention comprises an active inverter/rectifier system for a permanent magnet turbogenerator. In this embodiment, the system comprises a DC voltage link; a first active inverter/rectifier that comprises a connection for inputting or outputting a three-phase AC voltage from or to an AC voltage source, another connection for inputting or outputting a DC voltage from or to a DC voltage link, and at least six selectively switchable IGBTs, each having a corresponding anti-parallel diode, capable of boosting the DC voltage; and a second active inverter/rectifier that comprises a connection for inputting or outputting a three-phase AC voltage from or to a permanent magnet turbogenerator, another connection for inputting or outputting a DC voltage from or to the DC voltage link, and at least six selectively switchable IGBTs, each having a corresponding anti-parallel diode, capable of boosting the DC voltage wherein the boost capability of the first and the second active inverter/rectifiers comprises software and hardware controlled switch drivers.
Other embodiments comprising a different number of selectively switchable IGBTs and/or anti-parallel diodes are within the scope of the present invention.
A primary object of the present invention is to boost a DC link voltage.
A primary advantage of the present invention is increase operational efficiency of a permanent magnet turbogenerator.
Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.